Flux composition for solder, solder paste, and method of soldering

ABSTRACT

Soldering flux compositions, solder pastes, and methods of soldering using the same are provided, that exhibit excellent wettability, give highly reliable solder joints, and have superior storage stability. The flux composition contains at least one compound having at least one blocked carboxyl group selected from the group including compound (X) obtained by reaction of a carboxylic acid compound and a vinyl ether compound, compound (Y) obtained by reaction of a carboxylic acid anhydride compound and a hydroxy vinyl ether compound, and compound (Z) obtained by reaction of an acid anhydride and a polyhydric alcohol, followed by addition polymerization with a divinyl ether compound, and the flux composition is non-curing.

FIELD OF ART

[0001] The present invention relates to a flux composition, a solderpaste, and a method of soldering, used in mounting electronic componentson a printed circuit board or in soldering hybrid ICs (HICs).

BACKGROUND ART

[0002] Electronic components are mounted on printed circuit boardsmostly by soldering. Common soldering includes, prior to application ofa solder, removal with a flux of the oxide film on a metal surface to bejointed, and cleaning, or alternatively is implemented using a solderpaste containing solder powder in mixture with a flux.

[0003] Soldering fluxes are required to be highly insulative,noncorrosive, stable for a long time, and noncausative of materialproperty change of other parts, for maintaining good properties andreliability of the resulting products. On the other hand, for goodworkability, soldering fluxes are also required not to generate toxicgases, to give good solderability by removing oxides from and coveringthe metal surface and by lowering the surface tension of molten solder,not to be tacky, and to be easy to remove by cleaning.

[0004] A flux usually contains a resin, an activator, a solvent, andother additives, and is usually used by applying the flux to a surfaceof a metal substrate, or by soaking the substrate in the flux. A solderpaste is a viscous paste made of a solid or liquid flux and solderpowder kneaded together. The flux in a solder paste usually contains arosin compound, a thixotropic agent, an activator, a solvent, and adispersion stabilizer. As the base resin for the flux, a rosin compoundis used, such as natural rosin, polymerized rosin, hydrogenated rosin,or disproportionated rosin. As the activator for the flux, an organicacid is used, such as adipic, sebacic, or citric acid.

[0005] The carboxyl groups in the rosin compound and in the organic acidas an activator in the flux, function to remove metal oxides on a metalsurface to effectively improve solderability. However, such carboxylgroups form a post-solder residue, which adversely affects thereliability after soldering due to its ionic and mechanical effects. Ina solder paste containing a flux, the carboxyl groups also adverselyaffect the storage stability of the solder paste per se. Specifically,the flux component in a recent lead-free solder necessarily contains arelatively strong activator in a large amount for compensating forinferior wettability of the lead-free solder. However, such increasedactivity or amount of the activator impairs the reliability of thesolder joint, as well as the storage stability of the solder paste. Thuswettability required for the flux and the solder paste, and othernecessary properties such as reliability and storage stability areconflicting with each other, and all of these requirements are hard tobe fulfilled at the same time. Further, the kind and amount of theactivator need to be strictly limited.

[0006] As a flux remover, fluorinated or chlorinated solvents have beenin use, but their use is being limited for their impact on theenvironment. Hydrocarbon and alcohol solvents have also been in use,with problems in toxicity and inflammability. In this sense, water isthe most preferable defluxer, but no flux or solder paste has beenavailable that is sufficiently cleaned with water. When a flux is to becleaned with water, the non-volatile components of the flux must bewater-cleanable, and even the volatile solvent is preferablywater-cleanable, since a part of the solvent may be left over throughthe reflow. In general, rosin compounds used as a base resin for theflux component is hardly water-cleanable, and thus not usable in a fluxto be cleaned with water.

[0007] On the other hand, low-residue, no-clean fluxes with a low solidcontent are commercially available. However, reliability of suchno-clean fluxes is not yet sufficient when a resin molding or wirebonding process is to follow. Commercially available no-clean solderpastes are designed to have a lower solid content or no halide content,yet inevitably leave post-solder residues derived from the resincomponent such as rosin or the activator component. The residue from theactivator particularly has serious impact on the reliability. On thecontrary, the residue from the resin, such as rosin, does not have aserious effect on the soldering of most printed circuit boards forconsumer electric appliances and some kind of vehicle on-board printedcircuit boards. However, in soldering HICs, even a little residue willgive rise to terminal leakage or circuit corrosion of flip chips,leading to problems in the reliability in the following wire bondingstep.

[0008] For solving such problems, JP-2-290693-A and JP-2-25291-A proposea soldering method that leaves no residue, including reflowing a solderpaste with alcohol. The former discloses a paste containing solderpowder mixed with alcohols, such as monohydric alcohols, polyhydricalcohols, or ethers, with a boiling point about 30° C. higher than themelting point of the solder. This solder paste may be a residuelessmaterial, but may not be expected to have good wettability under anon-reducing atmosphere or at an ordinary reflow temperature.

[0009] JP-2001-239395-A proposes a thermosetting soldering fluxcontaining compound (A) having one or more blocked carboxyl groups in amolecule, and compound (B) having two or more reactive functional groupsin a molecule capable of forming chemical bonds with carboxyl groups byheating. However, since this flux contains the requisite compound (B)having two or more reactive functional groups, the compound (A) havingone or more blocked carboxyl groups is cured by thermal crosslinking.Thus this flux is a no-clean flux leaving a thermoset product, and thusis totally different from a flux requiring cleaning, or a no-clean,non-curing flux leaving substantially no residue, in its reaction,effects, and required properties.

SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide a solderingflux composition and a solder paste that exhibit excellent wettability,give highly reliable solder joints, and have superior storage stability.

[0011] It is another object of the present invention to provide asoldering flux composition and a solder paste that exhibit excellentwettability even under a non-reducing atmosphere or at an ordinaryreflow temperature, give highly reliable solder joints, and havesuperior storage stability.

[0012] It is yet another object of the present invention to provide amethod of soldering that enables easy application of solder thatexhibits excellent wettability and gives highly reliable solder joints.

[0013] According to the present invention, there is provided a solderingflux composition comprising at least one compound having at least oneblocked carboxyl group (sometimes referred to as compound (A)hereinbelow) selected from the group consisting of:

[0014] compound (X) obtained by reaction of a carboxylic acid compoundand a vinyl ether compound;

[0015] compound (Y) obtained by reaction of a carboxylic acid anhydridecompound and a hydroxy vinyl ether compound; and

[0016] compound (Z) obtained by reaction of an acid anhydride and apolyhydric alcohol, followed by addition polymerization with a divinylether compound,

[0017] wherein said soldering flux composition is non-curing.

[0018] According to the present invention, there is also provided asolder paste comprising the above-mentioned soldering flux compositionand solder powder.

[0019] According to the present invention, there is further provided amethod of soldering comprising the steps of:

[0020] (A) providing the above-mentioned flux composition on anelectrode portion of a substrate;

[0021] (B) providing a solder bumped electronic component;

[0022] (C) placing said electronic component provided in step (B) onsaid substrate obtained in step (A); and

[0023] (D1) subjecting said substrate with the electronic componentobtained in step (C) to reflow for mounting.

[0024] According to the present invention, there is also provided amethod of soldering comprising step (A) mentioned above, and step (D2)of supplying solder onto said substrate with the flux compositionobtained in step (A), by flowing or dipping.

[0025] According to the present invention, there is further provided amethod of soldering comprising the steps of:

[0026] (X) printing the above solder paste on an electrode portion of asubstrate;

[0027] (Y) placing an electronic component on said substrate obtained instep (X); and

[0028] (Z) subjecting said substrate with the electronic component toreflow for mounting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is an explanatory view illustrating the process formeasuring solder ball spread performed in Examples.

[0030]FIG. 2 is an explanatory schematic view illustrating the processfor mounting a flip chip IC in Example 3-1.

[0031]FIG. 3 is an explanatory schematic view illustrating the method ofsoldering by flow soldering in the flow step in Example 3-2.

[0032]FIG. 4 is an explanatory schematic view illustrating the method ofsoldering performed in Example 3-3.

[0033]FIG. 5 is a graph showing the results of the thermogravimetricanalysis of (S-4) and (A-1) used in the flux prepared in Example 1-17.

PREFERRED EMBODIMENTS OF THE INVENTION

[0034] The present invention will now be explained in detail.

[0035] The flux composition according to the present invention is anon-curing composition that contains compound (A) having at least oneblocked carboxyl group, and is free from a compound having two or morereactive functional groups in a molecule capable of forming chemicalbonds with carboxyl groups.

[0036] The compound (A) contains at least one compound selected from thegroup consisting of compound (X) obtained by reaction of a carboxylicacid compound and a vinyl ether compound, compound (Y) obtained byreaction of a carboxylic acid anhydride compound and a hydroxy vinylether compound, and compound (Z) obtained by reaction of an acidanhydride and a polyhydric alcohol, followed by addition polymerizationwith a divinyl ether compound.

[0037] Compound (X) may be a compound represented by the formula (1) or(2) below, wherein all the carboxyl groups are shown blocked, but somemay be left unblocked, as long as the objects of the present inventionare achieved.

[0038] In the formula (1), x is an integer of 1 to 6, A¹ stands for acarboxyl acid residue without —(COO—)_(x), and Z¹ stands for the formula(1-1) or (1-2):

[0039] wherein R¹, R², R³, R⁵, and R⁶ each independently stands for ahydrogen atom or an organic group having 1 to 50 carbon atoms, R⁴, R⁷,and R⁸ each independently stands for an organic group having 1 to 50carbon atoms, and Y¹ and Y² each independently stands for an oxygen orsulfur atom. In the formula (2), A² stands for a carboxylic acid residuewithout —(COO—)_(m). Y³ and Y⁴ each independently stands for an oxygenor sulfur atom, R⁹ stands for an organic group having 1 to 50 carbonatoms, m is an integer of 1 to 6, and n is an integer of 0 to 5.

[0040] The carboxylic acid compound as a starting material for compound(X) may be selected from monovalent aliphatic carboxylic acids, divalentor higher polyvalent aliphatic carboxylic acids, monovalent aromaticcarboxylic acids, and divalent or higher polyvalent aromatic carboxylicacids, with rosins and aliphatic dicarboxylic acids being particularlypreferred.

[0041] Examples of the carboxylic acid compound may include aliphaticcarboxylic acids, such as dicarboxylic acids including oxalic, malonic,succinic, adipic, glutaric, 2,4-diethylglutaric, 2,4-dimethylglutaric,pimelic, azelaic, sebacic, cyclohexanedicarboxylic, maleic, fumaric, anddiglycolic acids, fatty acids including caprylic, lauric, myristic,palmitic, stearic, arachic, behenic, linoleic, oleic, and linolenicacids, and hydroxycarboxylic acids including lactic, hydroxypivalic,dimethylolpropionic, citric, malic, and glyceric acids; aromaticcarboxylic acids such as benzoic, phthalic, isophthalic, trimellitic,and pyromellitic acids; and rosin compounds such as natural rosins,polymerized rosins, hydrogenated rosins, disproportionated rosins, andpartially modified rosins. Among these, natural and polymerized rosins,succinic, adipic, sebacic, glutaric, and 2,4-diethylglutaric acids arepreferred for their rheology, activity, and reliability.

[0042] The vinyl ether compound as a starting material for compound (X)may be selected from aliphatic vinyl ethers, aliphatic vinyl thioethers,cyclic vinyl ethers, and cyclic vinyl thioethers.

[0043] Examples of the aliphatic vinyl ethers may include monovinylether compounds such as methyl, ethyl, isopropyl, n-propyl, n-butyl,isobutyl, 2-ethylhexyl, and cyclohexyl vinyl ethers; divinyl ethercompounds such as butanediol, cyclohexanediol, cyclohexanedimethanol,diethyleneglycol, triethyleneglycol, tetraethyleneglycol,ethyleneglycol, and hexanediol divinyl ethers; trivinyl ether compoundssuch as trimethylolpropane trivinyl ether; and tetravinyl ethercompounds such as pentaerythritol tetravinyl ether. Examples of thealiphatic vinyl thioethers may include thio compounds corresponding tothe above examples of the aliphatic vinyl ethers.

[0044] Examples of the cyclic vinyl ethers may include 2,3-dihydrofuran,3,4-dihydrofuran, 2,3-dihydro-2H-pyran, 3,4-dihydro-2H-pyran,3,4-dihydro-2-methoxy-2H-pyran, 3,4-dihydro-4,4-dimethyl-2H-pyran-2-one,3,4-dihydro-2-ethoxy-2H-pyran, and 3,4-dihydro-2H-pyran-2-sodiumcarboxylate. Examples of the cyclic vinyl thioethers may include thiocompounds corresponding to the above examples of the cyclic vinylethers.

[0045] Among the above examples, n-propyl, n-butyl, 2-ethylhexyl vinylethers, and 1,4-butanediol divinyl ether are preferred for their readyavailability and the decomposition point of the resulting compound (X).The vinyl ethers may be compounds represented by the formula (5), (6),or (7):

[0046] wherein R¹ to R⁸ and Y¹ to Y³ are the same as above, R⁹ standsfor a residue derived from a polyfunctional vinyl ether compound, and his an integer of 2 to 8.

[0047] For producing a flux cleanable with an organic solvent, compound(X) in the present flux composition may be prepared from any of thecarboxylic acid compounds and any of the vinyl ether compounds as thestarting materials. For producing a water-cleanable flux, compound (X)in the flux composition may be prepared from a water-soluble carboxylicacid compound and any of the vinyl ether compounds as the startingmaterials, since the latter is to be volatized and thus imposes nolimitation. For producing a no-clean flux, compound (X) in the fluxcomposition may be prepared from a carboxylic acid compound having aboiling point of not higher than 300° C. and any of the vinyl ethercompounds as the starting materials, since the latter is to be volatizedand thus imposes no limitation. Further, for producing a no-clean fluxfrom the present flux composition containing a compound having onereactive functional group in a molecule capable of forming a chemicalbond with a carboxyl group upon heating, as will be discussed later,compound (X) in the flux composition may be prepared from any of thecarboxylic acid compounds and any of the vinyl ether compounds as thestarting materials.

[0048] For preparing compound (X), the carboxylic acid compound and thevinyl ether compound may be reacted, for example, at a reactiontemperature of 30 to 200° C., preferably 50 to 150°, for a duration of10 minutes to six hours, preferably 20 minutes to 5 hours. The end pointof the reaction may preferably be, for example, when the acid number ofthe reaction system is determined to be not larger than 5 mgKOH/g.Accordingly, the acid number of the reaction product is preferably notlarger than 5 mgKOH/g. It is particularly preferred to perform thereaction so that all of the carboxyl groups in compound (X) are blocked,but some of the carboxyl groups may be left unblocked, as long as theobjects of the present invention are achieved.

[0049] In the above-mentioned reaction, an acid catalyst may be used forpromoting the reaction. Further, an organic solvent may also be used forhomogenizing the reaction system to facilitate the reaction.

[0050] The acid catalyst for promoting the reaction may be, for example,an acidic phosphate represented by the formula (8):

[0051] wherein R¹⁵ stands for an alkyl, cycloalkyl, or aryl group having3 to 10 carbon atoms, and r is 1 or 2. Examples of the acidic phosphatemay include mono- or diesters of phosphoric acid and a primary alcoholsuch as n-propanol, n-butanol, n-hexanol, n-octanol, or 2-ethylhexanol,or a secondary alcohol such as isopropanol, 2-butanol, 2-hexanol,2-octanol, or cyclohexanol. As the acid catalyst, one or a combinationof two or more of the above may be used.

[0052] Examples of the organic solvent for homogenizing the reactionsystem to facilitate the reaction may include aromatic hydrocarbons suchas benzene, toluene, xylene, ethylbenzene, aromatic petroleum naphtha,tetralin, turpentine oil, and Solvesso #100 or #150 (trademarks of EXXONCHEMICAL CO.); ethers such as dioxane and tetrahydrofuran; esters andetheresters such as methyl acetate, ethylacetate, n-propyl acetate,isopropyl acetate, n-butyl acetate, isobutyl acetate, s-butyl acetate,amyl acetate, propyleneglycol monomethyl ether, triethyleneglycoldimethyl ether, tetraethyleneglycol dimethyl ether, diethyleneglycolmonobutyl ether acetate, and methoxybutyl acetate; ketones such asacetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amylketone, cyclohexanone, isophorone, methyloxide, methyl isoamyl ketone,ethyl butyl ketone, ethyl amyl ketone, diisobutyl ketone, diethylketone, methyl propyl ketone, and diisopropyl ketone; phosphates such astrimethyl phosphate, triethyl phosphate, and tributyl phosphate;dimethylsulfoxide, and N,N-dimethylformamide. As the organic solvent,one or a combination of two or more of the above may be used.

[0053] In the present flux composition, the content of compound (X) isusually 5 to 95 wt %, preferably 10 to 90 wt % of the total weight ofthe composition . With the content of less than 5 wt %, sufficientwettability is not given to the solder, whereas with the content of morethan 95 wt %, residues remain uncleaned to impair the reliability, thusbeing not preferred.

[0054] Compound (Y) may be a compound represented by the formula (3),wherein all the carboxyl groups are shown blocked, but some may be leftunblocked, as long as the objects of the present invention are achieved.Further, one of the hydroxyl group and the vinyl group of the hydroxyvinyl ether may have been reacted, while the other may be leftunreacted.

[0055] In the formula (3), R¹⁰ stands for a substituted or unsubstituteddivalent aliphatic or aromatic group having 1 to 50 carbon atoms, R¹¹stands for a divalent hydrocarbon group or glycol residue having 1 to 50carbon atoms, Y⁵ stands for an oxygen or sulfur atom, and s is aninteger of 1 to 500.

[0056] Compound (Y) may be prepared by reacting an acid anhydride, whichis an anhydride of carboxylic acid having two or more carboxyl groups ina molecule, and a hydroxy vinyl ether compound, which is a hydroxy vinylether having one vinyl ether group and one hydroxyl group in a molecule,or a hydroxy vinyl thioether having one vinyl thioether group and onehydroxyl group in a molecule.

[0057] The acid anhydride may be a compound represented by the formula(3-1), and the hydroxy vinyl ether compound may be a hydroxy vinyl etheror thioether represented by the formula (3-2):

[0058] wherein R¹⁰, R¹¹, and Y⁵ are the same as those in the formula (3)above.

[0059] Examples of the acid anhydride represented by the formula (3-1)may include succinic, maleic, itaconic, citraconic, tetrahydrophthalic,hexahydrophthalic, 4-methyltetrahydrophthalic,4-methylhexahydrophthalic, 3-methyltetrahydrophthalic,dodecenylsuccinic, phthalic, diglycolic, and glutaric anhydrides.

[0060] Examples of the hydroxyvinyl ether represented by the formula(3-2) may include hydroxymethyl, hydroxyethyl, hydroxypropyl,hydroxybutyl, hydroxypentyl, hydroxyhexyl, hydroxyheptyl, hydroxyoctyl,hydroxynonyl, 4-hydrocyclohexyl, 3-hydroxycyclohexyl, and2-hydrocyclohexyl vinyl ethers, and cyclohexanedimethanol,diethyleneglycol, triethyleneglycol, and tetraethyleneglycol monovinylethers. Examples of the hydroxy vinyl thioether represented by theformula (3-2) may include compounds corresponding to the above examplesof the hydroxy vinyl ether.

[0061] Compound (Y) may typically be derived from a succinic anhydrideand a hydroxy vinyl ether.

[0062] For producing a flux cleanable with an organic solvent, compound(Y) in the present flux composition may be prepared from any of the acidanhydrides and any of the hydroxy vinyl ethers as the startingmaterials. For producing a water-cleanable flux, compound (Y) in theflux composition may preferably be a reaction product of at least oneacid anhydride selected from the group consisting of succinic, maleic,diglycolic, itaconic, citraconic, and glutalic anhydrides, and at leastone hydroxy vinyl ether compound selected from the group consisting ofhydroxyethyl vinyl ether, hydroxypropyl vinyl ether, diethyleneglycolmonovinyl ether, and triethyleneglycol monovinyl ether. Here,“water-cleanable” as used herein means that compound (A), when added toa flux or a solder paste, is decomposed and removed by cleaning withwater, and that compound (A) per se is not necessarily water soluble.Further, “water-cleanable” is not limited to cleaning with water, andsemi-aqueous cleaners may also be used, such as water-alcohol,water-limonene, and water-glycol ether cleaners.

[0063] For producing a no-clean flux, compound (Y) may preferably be areaction product of at least one acid anhydride selected from the groupconsisting of tetrahydrophthalic, hexahydrophthalic,4-methyltetrahydrophthalic, and 4-methylhexahydrophthalic anhydrides,and at least one hydroxy vinyl ether compound selected from the groupconsisting of hydroxyethyl vinyl ether, hydroxypropyl vinyl ether,hydroxybutyl vinyl ether, hydroxypentyl vinyl ether, hydroxyethyl vinylthioether, hydroxypropyl vinyl thioether, and hydroxybutyl vinylthioether. Further, for producing a no-clean flux from the present fluxcomposition containing a compound having one reactive functional groupin a molecule capable of forming a chemical bond with a carboxyl groupupon heating, as will be discussed later, compound (Y) in the fluxcomposition may be prepared from any of the acid anhydrides and any ofthe hydroxy vinyl ethers as the starting materials.

[0064] The ratio of the acid anhydride to the hydroxy vinyl ethercompound for the reaction may be 1:0.5 to 5 in equivalence ratio. Thetemperature for the reaction is usually in the range from the roomtemperature to 200° C., preferably in the range from the roomtemperature to 150° C. The duration of the reaction may suitably beselected depending on the progress of the reaction, and may usually be 1to 100 hours. The end point of the reaction may preferably be, forexample, when the acid number of the reaction system is determined to benot larger than 20 mgKOH/g. Accordingly, the acid number of the reactionproduct is preferably not larger than 20 mgKOH/g. It is particularlypreferred to perform the reaction so that all of the carboxyl groups incomposition (Y) are blocked, but some of the carboxyl groups, such asthose at the terminals, may be left unblocked, as long as the objects ofthe present invention are achieved. Further, an acid catalyst, such asan acidic phosphate represented by the formula (8) above, may be usedfor promoting the reaction.

[0065] The amount of the acid catalyst is not particularly limited, andis usually 0.01 to 5 parts by weight, preferably 0.1 to 1 parts byweight based on 100 parts by weight of the acid anhydride and thehydroxy vinyl ether compound together.

[0066] The organic solvent may also be used here that was referred toabove as usable in the production of compound (X) for homogenizing thereaction system to facilitate the reaction. The amount of the organicsolvent is not particularly limited, and is usually 5 to 95 parts byweight, preferably 10 to 90 parts by weight, more preferably 20 to 80parts by weight based on 100 parts by weight of the acid anhydride andthe hydroxy vinyl ether together.

[0067] Compound (Y) may have a weight average molecular weight (Mw) ofusually 300 to 100000, preferably 500 to 50000. With Mw of lower than300, printability of the resulting solder paste prepared with thecompound is inferior, whereas with Mw of higher than 100000, many solderballs are disadvantageously formed.

[0068] In the present flux composition, the content of compound (Y), ifany, is not particularly limited, and is usually 5 to 95 wt %,preferably 10 to 90 wt % of the total weight of the composition.

[0069] Compound (Z) may be a compound represented by the formula (4)having in a molecule at least one hemiacetal group formed by addition ofcarboxylic acid to an unsaturated vinyl group, and ester groups ofcarboxylic acid and a hydroxyl group. In the formula (4), all thecarboxyl groups are shown blocked, but some may be left unblocked, aslong as the objects of the present invention are achieved. Further, atthe reactive terminal groups, one of the vinyl groups of the divinylether may have been reacted, and the other may remain as a double bond.

[0070] In the formula (4), R¹², R¹³, and R¹⁴ each independently standsfor a divalent organic residue, Y⁶ stands for an oxygen or sulfur atom,and t is an integer of 1 to 500.

[0071] Compound (Z) is prepared by addition polymerization of a reactionproduct of an acid anhydride and a polyhydric alcohol (sometimesreferred to as a modified carboxylic acid compound hereinbelow) with adivinyl ether compound, and may preferably be used for rendering a fluxcomposition water-cleanable. Compound (Z) may have a Mw of usually 500to 500000, preferably 1000 to 50000. With the Mw of lower than 500,printability of the resulting solder paste prepared with the compound isinferior, whereas with the Mw of higher than 500000, many solder ballsare disadvantageously formed.

[0072] The acid anhydride for preparing compound (Z) may be the acidanhydride represented by the formula (3-1) above, and the specificexamples referred to above may also be preferred here. Among theexamples, succinic, maleic, and itaconic anhydrides are preferred, withsuccinic anhydride being particularly preferred for its cleanabilitywith water, workability, and reactivity with polyhydric alcohols, aswell as for the solubility of the resulting compound in a solvent andits compatibility with other resins.

[0073] The polyhydric alcohol for preparing compound (Z) may be acompound represented by the formula (4-1):

HO—R¹³—OH   (4-1)

[0074] wherein R¹³ is the same as that in the formula (4) above.

[0075] Examples of the polyhydric alcohol may include ethylene glycol,diethylene glycol, triethylene glycol, tetraethylene glycol,1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol,1,4-butanediol, 2,3-butanediol, 1,6-hexanediol, pentanediol,dimethylbutanediol, trimethylolpropane, trimethylolethane, glycerine,and pentaerythritol, with ethylene, diethylene, and propylene glycolsbeing particularly preferred for their availability and reactivity.

[0076] The divinyl ether compound for preparing compound (Z) may be acompound represented by the formula (4-2):

CH₂═CH—Y⁶—R¹⁴—Y⁶—CH═CH₂   (4-2)

[0077] wherein Y⁶ and R¹⁴ are the same as those in the formula (4).

[0078] Examples of the divinyl ether compound may include diethyleneglycol divinyl ether, triethylene glycol divinyl ether,1,4-bisvinyloxymethylcyclohexene, ethylene glycol divinyl ether,polyethylene glycol divinyl ether, butanediol divinyl ether,1,4-cyclohexanedimethanol divinyl ether, and corresponding divinylthioethers, with diethylene glycol divinyl ether and butanediol divinylether being particularly preferred for their boiling point andreactivity.

[0079] Compound (Z) may preferably be prepared from a combination of thestarting materials such as a succinic, maleic, or itaconic anhydride, ora mixture thereof as the acid anhydride; ethylene, diethylene, orpropylene glycol, or a mixture thereof as the polyhydric alcohol; anddiethylene glycol or butanediol divinyl ether, or a mixture thereof asthe divinyl ether.

[0080] For producing a flux cleanable with an organic solvent, compound(Z) in the present flux composition may be prepared from any of thestarting materials without specific limitation. For producing awater-cleanable flux, compound (Z) in the flux composition maypreferably be prepared from at least one member selected from the groupconsisting of succinic, maleic, diglycolic, itaconic, citraconic, andglutalic anhydrides as the acid anhydride, and at least one memberselected from the group consisting of ethylene glycol, diethyleneglycol, triethylene glycol, tetraethylene glycol, 1,2-propylene glycol,1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol,trimethylolpropane, glycerine, and pentaerythritol as the polyhydricalcohol. For producing a no-clean flux, compound (Z) in the fluxcomposition may be prepared from any reaction product with a boilingpoint of not higher than 300° C. of the acid anhydride and thepolyhydric alcohol, and any divinyl ether compound, which is to bevolatized and thus imposes no limitation. Further, for producing ano-clean flux from the present flux composition containing a compoundhaving one reactive functional group in a molecule capable of forming achemical bond with a carboxyl group upon heating, as will be discussedlater, compound (Z) in the flux composition may be prepared from any ofthe starting materials without particular limitation.

[0081] The modified carboxylic acid compound for preparing compound (Z)may be prepared, for example, by reacting the acid anhydride and thepolyhydric alcohol without or in a suitable solvent at a temperaturefrom the room temperature to 200° C. The end point of the reaction maypreferably be when not less than 98% of the reaction has been determinedto be completed by measuring half and total acid numbers of theresulting resin.

[0082] The ratio of the modified carboxylic acid compound to the divinylether compound for the reaction may be usually 1.0:0.5to5.0, preferably1.0:1.0 to4.0, more preferably 1.0:1.0 to 3.0 in equivalence ratio.

[0083] For preparing compound (Z), the modified carboxylic acid compoundand the divinyl ether compound may be reacted, for example, at areaction temperature of 30 to 200° C., preferably 50 to 150° C, for aduration of 10 minutes to 6 hours, preferably 20 minutes to 5 hours. Theend point of the reaction may preferably be, for example, when the acidnumber of the reaction system is determined to be not larger than 10mgKOH/g, preferably not larger than 5 mgKOH/g. It is preferred toperform the reaction so that all of the carboxyl groups in compound (Z)are blocked, but some of the carboxyl groups, such as those at theterminals, may be left unblocked, as long as the objects of the presentinvention are achieved.

[0084] In the reaction, an acid catalyst may be used for promoting thereaction, and an organic solvent may also be used for homogenizing thereaction system to facilitate the reaction. Such acid catalyst andorganic solvent may be those exemplified in the discussion of compound(X) above. The solvent may be removed before the composition is used fora flux. However, in view of the productivity, it is preferred to use nosolvent, to use a water-cleanable solvent for the reaction, or to use asolvent decomposable or volatile under the conditions in which fluxes orsolder pastes are used. Examples of such solvent may include propyleneglycol monomethyl ether acetate and methyl ethyl ketone.

[0085] The amount of the acid catalyst is not particularly limited, andis usually 0.01 to 5.0 parts by weight, preferably 0.1 to 1.0 parts byweight, based on 100 parts by weight of the modified carboxylic acidcompound and the divinyl ether compound together. The amount of theorganic solvent is not particularly limited, and is 5 to 95 parts byweight, preferably 20 to 80 parts by weight, based on 100 parts byweight of the modified carboxylic acid compound and the divinyl ethercompound together.

[0086] The content of compound (Z), if any, in the flux composition isnot particularly limited, and is usually 10 to 100 wt %, preferably 50to 90 wt %. At less than 10 wt %, the intended effect is not obtained. Aurethane or polyester component, for example, may be bound to compound(Z).

[0087] In the flux composition according to the present invention,compounds (X) to (Z) as compound (A) may be combined and mixed for use.The combination and the mixing ratio may suitably be decided dependingon the application. For example, when the combination of compounds (Y)and (X) is used, the content of compound (X) may be 0.1 to 30 wt %,preferably 1 to 20 wt % of the total amount of the composition.

[0088] In compound (A) used in the present flux composition, the blockedcarboxyl groups are unblocked upon heating, or irradiation with activeenergy beams such as UV or electron beams, to expose reactive carboxylgroups. In the case of compound (Z), for example, the hemiacetal esterstructure in the principal chain is decomposed, and a corresponding lowmolecular weight compound is generated.

[0089] The decomposition is promoted by a latent heat catalyst orphotocatalyst, so that such catalysts may preferably be contained in thepresent flux composition.

[0090] Examples of the latent heat catalyst may include protonic acids,such as halogenocarboxylic acids, sulfonic acids, sulfuric acidmonoesters, phosphoric acid mono- and diesters, polyphosphoric acidesters, and boric acid mono- and diesters; compounds obtained byneutralizing a Lewis acid, such as BF₃, FeCl₃, SnCl₄, AlCl₃, and ZnCl₃,with a Lewis base; onium compounds; and mixtures thereof. Particularlypreferred are protonic acids, mixtures of a Lewis acid and atrialkylphosphate, sulfonic acid esters, phosphoric acid esters, oniumcompounds, and mixtures thereof.

[0091] More specific examples may include pyridine salts ofp-toluenesulfonic acid, pyridine salts of dodecylbenzene sulfonic acid,pyridine salts of naphthalene sulfonic acid, and pyridine salts ofnaphthalene disulfonic acid; metal halides, such as boron trifluoride,aluminum trichloride, titanium (II) chloride, titanium (III) oxide,ferrous chloride, ferric chloride, zinc chloride, zinc bromide, stannouschloride, stannic chloride, stannous bromide, and stannic bromide;organometallic compounds, such as trialkyl boron, trialkyl aluminum,dialkyl aluminum halide, monoalkyl aluminum halide, and tetraalkyltin;metal chelate compounds, such as diisopropoxy ethylacetoacetatealuminum, tris(ethylacetoacetate)aluminum, isopropoxybis(ethylacetoacetate)aluminum, monoacetyl acetonatobis(ethylacetoacetate)aluminum, tris(n-propylacetoacetate)aluminum,tris(n-butylacetoacetate)aluminum, monoethylacetoacetatebis(acetylacetonato)aluminum, tris(acetylacetonato)aluminum,tris(propyonylacetonato)aluminum, acetylacetonatobis(propyonylacetonato)aluminum, diisopropoxybis(ethylacetoacetate)titanium, diisopropoxybis(acetylacetonato)titanium, tetrakis(n-propylacetoacetate)zirconium,tetrakis(acetylacetonato)zirconium,tetrakis(ethylacetoacetate)zirconium, dichloro bis(acetylacetonato)tin,dibutylbis(acetylacetonato)tin, tris(acetylacetonato)iron,tris(acetylacetonato)chromium, tris(acetylacetonato)rhodium,bis(acetylacetonato)zinc, and tris(acetylacetonato)cobalt; and metalsoaps, such as dibutyltin dilaurate, dioctyltin ester maleate, magnesiumnaphthate, calcium naphthate, manganese naphthate, iron naphthate,cobalt naphthate, copper naphthate, zinc naphthate, zirconium naphthate,lead naphthate, calcium octylate, manganese octylate, iron octylate,cobalt octylate, zinc octylate, zirconium octylate, tin octylate, leadoctylate, zinc laurate, magnesium stearate, aluminum stearate, calciumstearate, cobalt stearate, zinc stearate, and lead stearate.

[0092] Examples of the photocatalyst may include β-ketosulfone,iminosulfonate, benzoinsulfonate, O-nitrobenzylsulfonate, and ADEKAOPTOMER SP Series (trade name, manufactured by ASAHI DENKA CO., LTD.).

[0093] One or a mixture of two or more of the latent heat catalysts orthe photocatalysts may be used, and the amount thereof is usually 0.01to 10 parts by weight, based on 100 parts by weight of compound (A).With the amount of less than 0.01 parts by weight, sufficient catalyticeffect cannot be obtained, whereas with the amount of more than 10 partsby weight, the low molecular weight compounds resulting from thedecomposition are undesirably colored, or side reaction may occur.

[0094] The flux composition according to the present invention mayoptionally contain, in addition to compound (A), at least one memberselected from the group consisting of activators, solvents, thixotropicagents, antioxidants, rust preventive agents, and chelating agents,depending on the required performance.

[0095] Examples of the activators may include amine salts ofhydrochloric and hydrobromic acids, carboxylic acid, and amine saltsthereof. More specific examples may include hydrochloride orhydrobromide of methyl, dimethyl, trimethyl, ethyl, diethyl, triethyl,n-propyl, di-n-propyl, tri-n-propyl, isopropyl, diisopropyl,triisopropyl, butyl, dibutyl, monoethanol, diethanol, and triethanolamines; oxalic, malonic, succinic, adipic, glutaric,2,4-diethylglutaric, 2,4-dimethylglutaric, pimelic, azelaic, sebacic,maleic, fumaric, lactic, diglycolic, capric, lauric, myristic, palmitic,linoleic, oleic, benzoic, hydroxypivalic, dimethylolpropionic, citric,malic, glyceric, stearic, arachic, behenic, and linolenic acids, andamine salts thereof.

[0096] The content of the activator, if any, is preferably 1 to 30 wt %,more preferably 1 to 20 wt % of the total weight of the composition.

[0097] The solvent may suitably be selected from ordinary solvents ofgeneral-purpose. Examples of the solvent may include aromatichydrocarbons such as toluene and xylene; alcohols such as methanol,ethanol, and isopropanol; esters such as ethyl acetate, ethyl lactate,and butyl acetate; ethers such as 1,4-dioxane and tetrahydrofuran;ketones such as methyl ethyl ketone, methyl isobutyl ketone, andcyclohexanone; glycol derivatives such as cellosolve and butylcellosolve; glycols such as ethylene glycol, diethylene glycol,dipropylene glycol, triethylene glycol, hexylene glycol, and1,5-pentanediol; glycol ethers such as methyl carbitol and butylcarbitol; and petroleum solvents such as petroleum ether and naphtha,with methyl ethyl ketone and 2-propanol being preferred.

[0098] The content of the solvent, if any, is preferably 5 to 95 wt % ofthe total weight of the composition.

[0099] The thixotropic agent may be of any kind. Examples of thethixotropic agent may include fatty acid amides such as castor wax,beeswax, carnauba wax, stearamide, and hydroxystearic acid bisamide;organic thixotropic agents such as low molecular weight polyethyleneglycol, high molecular weight polyethylene oxide, methyl cellulose,ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose,diglycerine monooleate, decaglycerine laurate, decaglycerine oleate,diglycerine monolaurate, and sorbitan laurate; and inorganic thixotropicagents such as silica powders and kaolin powders, with polyethyleneglycol, castor wax, and fatty acid amides being preferred.

[0100] The content of the thixotropic agent, if any, is preferably 1 to30 wt % of the total weight of the composition.

[0101] The content of the antioxidant and/or the rust preventive agent,if any, is preferably 0.01 to 30 wt % of the total weight of thecomposition.

[0102] Further, the flux composition according to the present inventionmay optionally contain matting agents, coloring agents, defoamingagents, dispersion stabilizers, and/or chelating agents.

[0103] An example of the flux composition according to the presentinvention may contain 5 to 95 wt % compound (A), 1 to 30 wt % activator,1 to 30 wt % thixotropic agent, 0.01 to 30 wt % antioxidant and/or rustpreventive agent, and 8 to 95 wt % solvent.

[0104] For producing a no-clean flux or a no-clean solder paste, theflux composition according to the present invention may optionallycontain a compound having one reactive functional group in a moleculecapable of forming a chemical bond with a carboxyl group upon heating(referred to as monofunctional compound (1) hereinbelow). Such amonofunctional compound, when contained in the composition, blocks thecarboxyl groups in the compound (A) and/or the activator left over afterthe process, to prevent adverse effects of the residual carboxyl groups.Thus the composition with the monofunctional compound may be used for ano-clean products.

[0105] Examples of the functional group in the monofunctional compoundmay include an epoxy group, an oxazoline residue, a silanol residue, analkoxysilane group, a hydroxyl group, an amino group, an imino group, anisocyanate group, a cyclocarbonate group, a vinyl ether group, a vinylthioether group, an aminomethylol group, an alkylated aminomethylolgroup, an acetal residue, and a ketal residue, with an epoxy group, anoxazoline residue, and a vinyl ether group being preferred.

[0106] Examples of the monofunctional compound having an epoxy group mayinclude glycidyl ethers of aliphatic alcohols having 1 to 20 carbonatoms such as methyl, butyl, 2-ethylhexyl, decyl, and stearyl glycidylethers; aromatic glycidyl ethers such as phenyl and t-butylphenylglycidyl ethers; and glycidyl esters of fatty acids having 2 to 20carbon atoms such as glycidyl laurate, glycidyl stearate, and glycidyloleate. Specifically preferred are glycidyl ethers of aliphatic alcoholshaving 12 to 20 carbon atoms, aromatic glycidyl ethers having 6 to 10carbon atoms, and glycidyl esters of fatty acids having 12 to 20 carbonatoms, for preventing generation of odor during working or the like.

[0107] Examples of the monofunctional compound having an oxazolineresidue may include 2-methyl-2-oxazoline, 4,4-dimethyl-2-oxazoline,5-methyl-2-oxazoline, 4,5-dimethyl-2-oxazoline, and4,4,5,5-tetramethyl-2-oxazoline. Examples of the monofunctional compoundhaving a vinyl ether group may include alkylvinyl ethers.

[0108] The content of the monofunctional compound, if any, is preferably0.1 to 50 parts by weight based on 100 parts by weight of compound (A)and the activator together.

[0109] The flux composition according to the present invention may beprepared by any method. For example, the flux composition may beprepared by blending all the materials together, or by taking thesolvent in a container, and mixing and dissolving other materialstherein one after another. For mixing, for example, a vacuum mixer, akneader, a homodisper, or a three-one motor may be used. The mixing maybe performed at any temperature and under any conditions, but preferablyperformed at 10 to 30° C. in a clean room.

[0110] The solder paste according to the present invention contains theflux composition and solder powder.

[0111] The solder powder may be of any kind, and for example, ofconventional Sn/Pb, Sn/Ag, Sn/Ag/Cu, Sn/Cu, Sn/Zn, Sn/Zn/Bi,Sn/Zn/Bi/In, Sn/Bi, or Sn/In alloy. The solder particle may either be ofspherical or amorphous shape, and may be of any ordinary diameter. Inthe case of spherical particles, the diameter is preferably 20 to 60 μm.

[0112] The solder powder may have any alloy composition. Preferredexamples may include Sn63/Pb37, Sn/Ag3.5, Sn/Ag3.5/Cu0.5,Sn/Ag2.9/Cu0.5, Sn/Ag3.0/Cu0.5, Sn/Bi58, Sn/Cu0.7, Sn/Zn9, andSn/Zn8/Bi3, wherein the values indicate the weight ratio of the metals.For avoiding problems associated with solder disposal, such as airpollution by lead, lead-free solders are preferred. The content of theflux in the solder paste is usually 1 to 50 wt %, specifically 5 to 30wt %, more specifically 5 to 15 wt % of the total weight of the solderpaste. With less than 50 wt % or more than 99 wt % solder powder,required solder printability is not obtained, thus not being preferred.In view of recent environmental problems and recycling, lead-free solderpastes are preferred.

[0113] The solder paste according to the present invention may beprepared by kneading and mixing the solder powder with the fluxcomposition by an ordinary method. For mixing, for example, a vacuummixer, a kneader, or a planetary mixer may be used. The mixing may beperformed at any temperature and under any conditions, but preferablyperformed at 5 to 25° C. in a nitrogen atmosphere. The mixing ratio ofthe flux composition to the solder powder is not particularly limited,and is usually 5 to 20:80 to 95 by weight.

[0114] The solvent used as needed for preparing the solder paste maypreferably be those having a boiling point of not lower than 150° C.Examples of the solvent may include triethylene glycol monomethyl ether,triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether,diethylene glycol monomethyl ether, diethylene glycol monobutyl ether,diethylene glycol monohexyl ether, ethylene glycol monophenyl ether,diethylene glycol monophenyl ether, diethylene glycol monobutyl acetate,dipropylene glycol, diethylene glycol-2-ethylhexyl ether, α-terpineol,benzyl alcohol, 2-hexyldecanol, butyl benzoate, diethyl adipate, diethylphthalate, dodecane, tetradecene, dodecylbenzene, ethylene glycol,diethylene glycol, dipropylene glycol, triethylene glycol, hexyleneglycol, 1,5-pentanediol, methyl carbitol, and butyl carbitol, withtriethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether,and diethylene glycol monobutyl acetate being preferred.

[0115] The solder paste according to the present invention mayoptionally contain an antioxidant, a matting agent, a coloring agent, adefoaming agent, a dispersion stabilizer, and/or a chelating agent.

[0116] The solder paste according to the present invention may be usedas a solder for a reflow solder process in the production of electroniccomponents, electronic modules, and printed wiring boards, by printingthe solder paste through a metal mask using a solder printer inaccordance with an ordinary method. Specifically, the followingsoldering method according to the present invention is preferred.

[0117] The methods of soldering according to the present invention are amethod including the steps of (A) providing the flux composition on anelectrode portion of a substrate, (B) providing a solder bumpedelectronic component, (C) placing the electronic component provided instep (B) on the substrate obtained in step (A), and (D1) subjecting thesubstrate with the electronic component obtained in step (C) to reflowfor mounting; a method including step (A), and step (D2) of supplyingsolder onto the substrate with the flux composition obtained in step(A), by flowing or dipping; and a method including the steps of (X)printing the solder paste of the present invention on an electrodeportion of a substrate, (Y) placing an electronic component on thesubstrate obtained in step (X), and (Z) subjecting the substrate withthe electronic component to reflow for mounting.

[0118] In the methods of soldering according to the present invention,each step may be performed by an ordinary method under ordinaryconditions, as long as the flux composition or the solder pasteaccording to the present invention is used as the flux or the solderpaste.

[0119] In the methods of soldering according to the present invention, acleaning step with water may be performed in addition to the abovesteps, when the water-cleanable flux composition or solder paste of thepresent invention is used in the method, whereas no such cleaning stepis required when the no-clean flux composition or solder paste of thepresent invention is used.

[0120] Since the flux composition according to the present inventioncontains compound (A), which gives a carboxylic acid compound of a lowmolecular weight when thermally decomposed, the composition has a highflux activity, gives excellent reliability to resulting joints, and maybe prepared with a reduced amount of solvent. Further, in the solderpaste according to the present invention, the base resin or theactivator is excellently inhibited from being reacted with the solderpowder in the solder paste, which is reduced in average particle size tokeep up with the downsizing of electronic products or fine pitchrequirements. Thus the solder paste of the present invention hasexcellent storage stability, as well as wettability. Specifically,wettability and storage stability of a conventional lead-free, Sn/Znsolder paste may be improved, which paste has hardly been usedpractically due to its extremely poor wettability and storage stability.Further, since the composition of the present invention is non-curing,and thus little or no flux residue occurs, the present composition isextremely useful for preparing, for example, fluxes for soldering ICchips directly to a silicon wafer, flowing fluxes, and dipping fluxes,in which applications thermosetting fluxes cannot be used.

EXAMPLES

[0121] The present invention will now be explained in detail withreference to examples, but the present invention is not limited thereto.

[0122] In the following examples, the acid number was determined bydissolving a predetermined amount of resin in a THF solution, andtitrating with a KOH/ethanol solution, using phenolphthalein as anindicator, in accordance with JIS K 0070-3 (1992). The viscosity wasmeasured with an EHD viscometer manufactured by TOKI SANGYO CO., LTD, atthe revolution of 0.5 to 100 rpm at 25° C. for 3 minutes. Thedecomposition point was measured with “TG/DTA220” manufactured by SEIKOINSTRUMENTS INC., at the heating rate of 10° C./min, at the nitrogenflow rate of 50 ml/min. The weight average molecular weight (Mw) wasmeasured using a gel permeation chromatography system, SC-8010 (GPC)manufactured by TOSOH CORPORATION, “SHODEX K-801” manufactured by SHOWADENKO K.K. as a column, THF as an eluent, and a RI detector, anddetermined in terms of polystyrene standards.

[0123] Further in the examples, “natural rosin” refers to “CHUGOKU ROSINX” (trade name) manufactured by HARIMA CHEMICALS, INC., “hydrogenatedrosin” refers to “PINE CRYSTAL KE-604” (trade name) manufactured byARAKAWA CHEMICAL INDUSTRIES, LTD., 2-EHVE refers to 2-ethylhexyl vinylether, n-PVE refers to n-propyl vinyl ether, n-BuVE refers to n-butylvinyl ether, TEGDVE refers to triethylene glycol divinyl ether,1,4-BDDVE refers to 1,4-butanediol divinyl ether, PMA refers topropylene glycol monomethyl ether acetate, “RIKACID MH-700” (trade name)refers to a mixture of hexahydrophthalic anhydride andmethylhexahydrophthalic anhydride manufactured by NEW JAPAN CHEMICALCO., LTD., HEVE refers to hydroxyethyl vinyl ether, HBVE refers tohydroxybutyl vinyl ether, DEGMVE refers to diethylene glycol monovinylether, the acid catalyst is a zinc complex prepared by reacting zincoctylate and triethanol amine at an equal molar ratio, “EPIOL SK” (tradename) refers to stearyl glycidyl ether manufactured by NOF CORPORATION,DEGHE refers to diethylene glycol hexyl ether, BCA refers to butylcarbitol acetate, PEG refers to polyethylene glycol, and TEG refers totriethylene glycol.

Synthesis Example 1

[0124] 321 g of natural rosin and 209 g of 2-EHVE were placed in afour-neck flask of 1 liter capacity equipped with a thermometer, areflux condenser, and a stirrer. The mixture was heated from an ordinarytemperature to 120° C. over 30 minutes, and reacted at 120° C. for 2.5hours. When the acid number was confirmed to be not higher than 5mgKOH/g, the reaction was terminated. Then unreacted 2-EHVE wasdistilled off with a rotary evaporator, to obtain a clear brown rosinderivative (R-1) having a viscosity of 6.8 poise. The composition andthe reaction conditions, as well as the obtained amount, yield, acidnumber, viscosity, and decomposition point of the rosin derivative (R-1)are shown in Table 1.

Synthesis Examples 2 to 4

[0125] Rosin derivative (R-2) and vinyl ether-blocked adipic acid (A-1)and (A-2) were prepared in the same way as in Synthesis Example 1,except that the composition and the reaction conditions were changed asshown in Table 1. The properties of (R-2), (A-1), and (A-2) are shown inTable 1. TABLE 1 Syn. 1 Syn. 2 Syn. 3 Syn. 4 Product (code) (R-1) (R-2)(A-1) (A-2) Composition Natural rosin 321 — — — in parts by Hydrogenatedrosin — 502 — — weight Adipic acid — — 260 — 2,4-diethylglutaric — — —309 acid 2-EHVE 209 — — — n-PrVE — — 267 — n-BuVE — — — 491 TEGDVE — 298— — Reaction Temperature (° C.) 120 100 100 100 conditions Duration(hrs) 2.5 2.0 2.5 4.0 Amount obtained (g) 325 504 312 400 Yield (%) 6163 59 50 Acid number (mgKOH/g) 4.5 3.9 2.1 2.5 Viscosity (pois) 6.8 1.50.1 0.8 Decomposition point (° C.) 193 236 165 188

Synthesis Examples 5 and 6

[0126] Monomers having a composition shown in Table 2 were placed in afour-neck flask equipped with a thermometer, a reflux condenser, and astirrer. The mixture was stirred into homogeneity at 60° C., heated to140° C., and kept reacting at this temperature. When not less than 98%of the reaction had been completed, which was confirmed by measuring thehalf acid number and the total acid number of the resin, the reactionwas terminated. Then, the solvent was removed from the reaction productunder reduced pressure, to obtain a half ester compound of diol and anacid anhydride, i.e., a derivative of dicarboxylic acid half ester (H-1)and (H-2). TABLE 2 Syn. 5 Syn. 6 Product (code) (H-1) (H-2) Compositionin Succinic anhydride 58.3 48.9 parts by weight Ethylene glycol 21.7 —Diethylene glycol — 31.1 Methyl ethyl ketone 20.0 20.0

Synthetic Examples 7 to 10

[0127] Monomers having a composition shown in Table 3 were placed in afour-neck flask equipped with a thermometer, a reflux condenser, and astirrer. The mixture was heated from an ordinary temperature to 120° C.over 30 minutes, and kept reacting at 120° C. When the acid number aftermixing became not more than 10 mgKOH/g, or the infrared absorptionspectrum at 3543 cm⁻¹ corresponding to the hydroxyl group in thecarboxyl group disappeared, the reaction was terminated. After thetermination of the reaction, unreacted divinyl ether and the solventwere distilled off with a rotary evaporator, to obtain a polyhemiacetalester resin (P-1) to (P-4). The properties of these resins are shown inTable 3. TABLE 3 Syn. 7 Syn. 8 Syn. 9 Syn. 10 Product code (P-1) (P-2)(P-3) (P-4) Starting Adipic acid 32.5 — — — Material 2,4-diethylglutaric— 30.6 — — Composition acid in parts by (H-1) — — 51.0 — weight (H-2) —— — 50.7 TEGDVE — 39.4 — — 1,4-BDDVE 67.5 — 29.0 29.3 PMA — 30.0 20.020.0 Yield (%) 63.0 61.9 62.8 61.5 Acid number (mgKOH/g) 9.3 8.5 3.2 4.3Viscosity (Pa · s) 3.4 5.5 6.0 4.8 Decomposition point (° C.) 224.0243.7 239.3 239.9 Weight average molecular weight 13000 60200 9700 11400(Mw)

Synthesis Examples 11 to 14

[0128] Monomers having a composition shown in Table 4 were placed in afour-neck flask equipped with a thermometer, a reflux condenser, and astirrer. The mixture was heated from an ordinary temperature to 110-120°C. over 30 minutes, and reacted at 110 to 120° C. for 4 hours. When theacid number after mixing was confirmed to be not more than 20 mgKOH/g,the reaction was terminated. Then the polymer component was purified byreprecipitation with a hexane/acetone (9/1 in volume ratio) mixedsolvent. After the solvent was distilled off of the mixed solution witha rotary evaporator, the reaction product was vacuum dried with a vacuumpump, to obtain a clear, light yellow resin having the properties shownin Table 4. TABLE 4 Syn. 11 Syn. 12 Syn. 13 Syn. 14 Product code (S-1)(S-2) (S-3) (S-4) Composition Succinic anhydride 24.3 22.2 19.2 — inparts by RIKACID MH-700 — — — 34.2 weight HEVE 63.7 — — 35.8 HBVE — 51.6— — DEGMVE — — 50.8 — PMA 12.0 26.2 30.0 30.0 Yield (%) 59.7 56.8 55.645.9 Acid number (mgKOH/g) 15.3 12.1 17.5 15.3 Viscosity (pois) 358 337306 5200 Decomposition point (° C.) 203 202 216.1 227.1 Weight averagemolecular weight 4900 8900 5400 6300 (Mw)

Examples 1-1 to 1-9

[0129] A flux having a composition shown in Table 5 was prepared, usingeach blocked carboxylic acid compound prepared in Synthesis Examples.The obtained flux was evaluated by the following testing and evaluatingmethods. The results are shown in Table 5

[0130] <Evaluation of Solder Ball Spread>

[0131] Solder ball spread was measured in accordance with the measuringmethod shown in FIG. 1. That is, solder ball 10a having a diameter of0.-76 mm and flux 10 b to be measured were placed on thick film Cuconductor 11 (FIG. 1(a)), and reflowed at the peak temperature in theatmosphere (FIG. 1(b)). The diameter of the resulting, spread solderball was determined in percentage to the average value Z. Here, thesolder ball does not always spread evenly as shown in FIG. 1(c), so thatthe average value of spread Z (Z=(X+Y)/2) was calculated, and the spreadwas determined as ((Z−0.76)/0.76)×110 (%).

[0132] The solder balls used here was manufactured by MITSUI MINING &SMELTING CO., LTD. Evaluation of solder ball spread (1) (referred to asevaluation (1) hereinbelow) was made using Sn63/Pb37 (weight ratio)solder balls with the peak temperature of 220° C., evaluation (2) wasmade using Sn/Ag2.9/Cu0.5 (weight ratio) solder balls with the peaktemperature of 240° C, and evaluation (3) was made using Sn/Zn8.0/Bi3.0(weight ratio) solder balls with the peak temperature of 230° C.

[0133] <Evaluation of Cleanability of Residue>The flux was applied to a50 mm×50 mm×1.6 mm comb-shaped substrate having a conductor width of0.318 mm, a conductor spacing of 0.318 mm, and an overlap length of15.75 mm. After the reflow, the substrate was soaked in D-limonene ordeionized water adjusted to 30° C. for 5 minutes in ultrasonic waves,and dried. The substrate was visually observed, and the degree ofresidue was evaluated on three levels; (a) no residue was observedvisually, (b) slight residue was observed, and (c) residue was clearlyobserved. The evaluation with D-limonene was identified as cleanability(1), and that with deionized water as cleanability (2).

[0134] <Evaluation of Insulation Performance>

[0135] An insulation resistance test was conducted in accordance withJIS Z 3197. Resistance of not lower than 10¹¹ Ω was indicated as (a),resistance not lower than 10⁹ Ω and lower than 10¹¹ Ω was indicated as(b), and resistance lower than 10⁹ Ω was indicated as (c). TABLE 5Example 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 Composition (R-1) 16 72 — —— — — — — in parts by (R-2) — — 25 — — — 10 10 10 weight (P-1) 18 18 — —— — — — — (P-2) — — — 25 — — — — — (S-1) — — — — 25 — 15 15 15 (S-2) — —— — — 25 — — — (A-1) — — — —  5  5 — — — (A-2) — —  5  5 — —  5  5  5Castor —  6 — — — — — — — wax Acid — — — — — — —   0.1 — catalyst EPIOLSK — — — — — — — —  5 Methyl 66 — — — — — — — — ethyl ketone DEGHE — — —— 70 70 — — — BCA — 70 70 70 — — 70 70 65 Result of Evaluation 85 85 9089 89 89 89 90 89 Evaluation (1) (%) Evaluation 82 82 85 83 87 87 82 8385 (2) (%) Evaluation 12 15 80  8 85 85 11 12 80 (3) (%) Clean- (a) (a)(a) (a) (a) (a) (a) (a) (a) ability (1) Insulation (a) (a) (a) (a) (a)(a) (a) (a) (a) Perfor- mance

Examples 1-10 to 1-17

[0136] A flux having a composition shown in Table 6 was prepared, usingeach blocked carboxylic acid compound prepared in Synthesis Examples.The obtained flux was evaluated in the same way as in Examples 1-1 to1-9. In Examples 1-14 and 1-17, the following evaluation of residueafter reflow was made in stead of the evaluation of cleanability. Theresults are shown in Table 6.

[0137] <Evaluation of Residue after Reflow>The flux was applied to asubstrate similar to the comb-shaped substrate used in the evaluation ofcleanability, and subjected to reflow. Then the substrate was visuallyobserved, and the degree of residue was evaluated on three levels as inthe evaluation of the cleanability. TABLE 6 Example 1-10 1-11 1-12 1-131-14 1-15 1-16 1-18 Composition (P-3) 90 — — — — — — — in parts by (P-4)— 90 — — — — — — weight (S-1) — — 25 — — 25 25 — (S-3) — — — 25 — — — —(S-4) — — — — 25 — — 25 (A-1) 10 10  5  5  5  5  5  5 PEG4000 — — — — —10 — — Acid catalyst — — — — — —   0.1   0.1 TEG — — 70 70 — 60 70 — PMA— — — — 70 — — 70 Result of Evaluation (1) (%) 86 85 89 85 89 85 89 89Evaluation Evaluation (2) (%) 81 80 87 84 89 85 87 89 Evaluation (3) (%)12 15 80  8 85 85 11 12 Residue after — — — — (a) — — (a) reflowCleanability (2) (a) (a) (a) (a) — (a) (a) — Insulation (a) (a) (a) (a)(a) (a) (a) (a) Performance

Comparative Examples 1-1 to 1-7

[0138] A flux was prepared using commercially available materials at apredetermined ratio as shown in Table 7. The obtained flux was subjectedto the same evaluations as in Examples 1-1 to 1-17. The results areshown in Table 7. TABLE 7 Comparative Example 1-1 1-2 1-3 1-4 1-5 1-61-7 Composition Natural rosin 12 — 13 13 — — — in parts by Polymerizedrosin  5 25 12 12 — — — weight Hydrogenated rosin  2 — — — — — — PEG4000— — — — 50 — — Glycerine — — — — — 50 100  Adipic acid  5  5  5 —  5 — —Propylamine-HBr — — —  1 —  5 — 2-Propanol 77 70 70 74 — — — TEG — — — —45 45 — Result of Evaluation (1) (%) 85 85 84 86 75 77 60 EvaluationEvaluation (2) (%) 82 76 72 80 65 60 46 Evaluation (3) (%) 10 10 13 20 5  5  0 Residue after — — — — — — (a) reflow Cleanability (1) (a) (a)(a) (a) — — — Cleanability (2) — — — — (b) (a) — Insulation (a) (b) (b)(c) (b) (a) (a) Performance

Examples 2-1 to 2-23

[0139] A solder paste was prepared by kneading a flux having acomposition shown in Tables 8 and 9 with fine pitch solder powder(solder powder type (1) (Sn63/Pb37 (weight ratio))), solder powder type(2) (Sn/Ag2.9/Cu0.5 (weight ratio)), or solder powder type (3)(Sn/Zn8/Bi3 (weight ratio)), having an average particle size of 25 μmand manufactured by MITSUI MINING AND SMELTING CO., LTD. The obtainedsolder paste was evaluated for wettability, solder ball test, voidformation, insulation performance, storage stability, and cleanabilityof residue. The results are shown in Tables 8 and 9.

[0140] <Evaluation of Wettability>

[0141] The test was conducted in accordance with JIS Z 3284, Appendix10. The evaluation was made on the following 1 to 4 scale of spread.

[0142] 1: Solder melted from the solder paste wetted the test plate, sothat the solder spread into the area that was larger than the area towhich the solder paste was originally applied.

[0143] 2: The whole area to which the solder paste was originallyapplied was wet with solder.

[0144] 3: Most of the area to which the solder paste was originallyapplied was wet with solder (including the dewetted state).

[0145] 4: No wetting of the test plate with solder was observed, and themolten solder formed one or more solder balls (non-wetted state).

[0146] <Solder Ball Test (Degree of Solder Coalescence)>

[0147] The test was conducted in accordance with JIS Z 3284, Appendix11. The evaluation was made on the following 1 to 4 scale of spreading.

[0148] 1: Solder powder was molten to form one large ball, without anysolder balls therearound.

[0149] 2: Solder powder was molten to form one large ball, with not morethan three solder balls having a diameter of not larger than 75 μmarranged therearound.

[0150] 3: Solder powder was molten to form one large ball, with not lessthan four solder balls having a diameter of not larger than 75 μmarranged therearound but not in a semi-continuous halo.

[0151] 4: Solder powder was molten to form one large ball, with a numberof smaller solder balls arranged therearound in a semi-continuous halo.

[0152] 5: Other than 1 to 4.

[0153] <Evaluation of Void Formation (Reliability of Joint)>

[0154] The solder paste was printed on a 60 mm² copper plate in six 6mm-diameter patterns through a metal mask of 150 μm thick, and reflowedunder an air atmosphere. Then the copper plate with the solder was cutwith a cutter, and the soldered portion was observed under a microscopefor void formation. The six patterns were measured for voids of 10 μm orlarger. The solder pastes having the average number of voids of lessthan two per pattern were indicated as passed, and those having theaverage number of voids of two or more per pattern were indicated asfailed.

[0155] <Insulation Performance>

[0156] An insulation resistance test was conducted in accordance withJIS Z 3284. Resistance of not lower than 10¹¹ Ω was indicated as (a),resistance not lower than 10⁹ Ω and lower than 10¹¹ Ω was indicated as(b), and resistance lower than 10⁹ Ω was indicated as (c).

[0157] <Evaluation of Storage Stability>

[0158] An accelerated test was conducted by storing the produced solderpaste at 25° C. for 7 days, and evaluation was made based on the ratioof the viscosity of the paste immediately after production to theviscosity after the accelerated test as an index. The conditions of theaccelerated test generally correspond to cold storage at 5° C. for threemonths. The viscosity was measured using a spiral viscometermanufactured by MALCOM CO., LTD. under the conditions for the spiralmethod in accordance with JIS z 3284.

[0159] <Evaluation of Cleanability of Residue>

[0160] The solder paste was applied to a 50 mm×50 mm×1.6 mm comb-shapedsubstrate having a conductor width of 0.318 mm, a conductor spacing of0.318 mm, and an overlap length of 15.75 mm. After the reflow, thesubstrate was soaked in a cleaning liquid adjusted to 30° C. for 5minutes in ultrasonic waves, and dried. The substrate was visuallyobserved, and the degree of residue was evaluated on three levels. Theoscillating frequency of the ultrasonic waves was 38 kHz.

[0161] The substrates with no residue observed visually were indicatedas (a), those with slight residue observed were indicated as (b), thosewith residue clearly observed were indicated as (c). The evaluation withD-limonene was identified as cleanability (1), that with deionized wateras cleanability (2), and that with deionized water/isopropanol (80/20 byvolume ratio) as cleanability (3).

[0162] <Evaluation of Residue after Reflow>The solder paste was appliedto a substrate similar to the comb-shaped substrate used in theevaluation of cleanability, and subjected to reflow. Then the substratewas visually observed, and the degree of reside was evaluated in thesame way as in the evaluation of the cleanability. TABLE 8 Example 2-12-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 2-11 2-12 Flux (R-1) 6   6   6   —— — — — — — — — composition (R-2) — — — 6   — — — — — 2   2   2   inparts (P-1) 2   — — — — — — — — — — — by (P-2) — — — — 6   — — — — — — —weight (S-1) — — — — — 7   7   7   — 5   5   5   (S-2) — — — — — — — —7   — — — (A-1) — 2   2   — — 0.5 0.5 0.5 0.5 — — — (A-2) — — — 2   2  — — — — 1   1   1   Castor wax 0.8 0.8 0.8 — — — — — — — — —Hydrogenated — — — 1   — 1   1   1   1   1   1   1   castor oil Acidcatalyst — — — — — — — — — 0.1 0.1 0.1 EPIOL SK — — — — — — — — — — —1   Benzotriazole — — — — — — — — — 0.5 0.5 0.5 2-Propanol 1.2 1.2 1.2 —— — — — — — — — DEGHE — — — — — 2   2   2   2   — — — BCA — — — 1   1  — — — — 1   1   — Type of solder powder (2) (3) (1) (2) (2) (1) (2) (3)(3) (2) (3) (2) Amount of solder powder 90   90   90   90   90   90  90   90   90   90   90   90   (parts by weight) Result of Wettability1   2   2   1   1   1   1   1   1   1   1   1   Evaluation Solder balltest 1   1   1   1   1   1   1   1   1   1   1   1   Void formationpassed passed passed passed passed passed passed passed passed passedpassed passed Insula- Initial (a) (a) (a) (a) (a) (a) (a) (a) (a) (a)(a) (a) tion After 100 (a) (a) (a) (a) (a) (a) (a) (a) (a) (a) (a) (a)Perfor- hrs mance Storage Initial 230    235    245    231    236   480    500    520    550    225    230    229    stability After 100240    236    249    235    238    490    520    550    570    226   235    235    (Pa · s) hrs Viscosity  1.04  1.01  1.02  1.02  1.01  1.02 1.04  1.06  1.04  1.00  1.02  1.03 Increase Ratio Residue cleanability(a) (a) (a) (a) (a) (a) (a) (a) (a) (a) (a) (a) (1)

[0163] TABLE 9 Example 2-13 2-14 2-15 2-16 2-17 2-18 2-19 2-20 2-21 2-222-23 Flux (P-3) 8.5 8.5 8.5 — — — — — — — — composition in (S-2) — — — 77 7 — — 6 6 6 parts by weight (S-3) — — — — — — 7 — — — — (S-4) — — — —— — — 7 — — — (A-1) 1   1   1   0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 PEG 40000.5 0.5 0.5 — — — — — — — — PEG 6000 — — — 1   1   1   1   — 1   1   1  Trimethylolpropane — — — — — — — 1   — — — Acid catalyst — — — — — — — —0.1 0.1 0.1 Benzotriazole — — — — — — — — 0.5 0.5 0.5 TEG — — — 2   2  2   2   — 2   2   2   Butyl carbitol — — — — — — — 2   — — — Type ofsolder powder (1) (2) (3) (1) (2) (3) (2) (2) (1) (2) (3) Amount ofsolder powder 90   90   90   90   90   90   90   90   90   90   90  (parts by weight) Result of Wettability 1   1   1   1   1   1   1   1  1   1   1   Evaluation Solder ball test 1   1   1   1   1   1   1   1  1   1   1   Void formation passed passed passed passed passed passedpassed passed passed passed passed Insulation Initial (a) (a) (a) (a)(a) (a) (a) (a) (a) (a) (a) Performance After 100 hrs (a) (a) (a) (a)(a) (a) (a) (a) (a) (a) (a) Storage Initial 230    235    245    400   430    470    490    395    225    230    229    stability After 100 hrs240    236    249    420    460    500    520    420    226    235   235    (Pa · s) Viscosity  1.04  1.01  1.02  1.05  1.07  1.06  1.06 1.06  1.00  1.02  1.03 Increase Ratio Residue after reflow — — — — — —— (a) — — — Residue cleanability (1) (a) (a) (a) (a) (a) (a) (a) — (a)(a) (a)

Comparative Examples 2-1 to 2-9

[0164] A solder paste was prepared by mixing and kneading commerciallyavailable materials and one of the various solder powders at apredetermined ratio as shown in Table 10. The obtained solder paste wassubjected to the same evaluations as in Examples 2-1 to 2-23. Theresults are shown in Table 10.

[0165] Incidentally, the viscosity after 100 hours as evaluation of thestorage stability in Comparative Examples 2-4 and 2-7 was too high to bemeasured. TABLE 10 Comparative Example 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-82-9 Flux composition Natural rosin 2.5 — — — — — — — — in parts byweight Polymerized rosin 2.5 6   6   6   — — — — — PEG 1000 — — — — 6  6   6   — — Tetraethylene glycol — — — — — — — 9   — Glycerine — — — — —— — — 9   Adipic acid 0.6 1   1   1   1   1   1   — — Castor wax 0.8 — —— — — — — — Hydrogenated castor oil — 1   1   1   — — — — — Hydroxyethylcellulose — — — — 1   1   1   — — Trimethylol propane — — — — — — — 1  1   DEGHE 3.5 2   2   2   — — — — — TEG — — — — 2   2   2   — — Type ofsolder powder (2) (1) (2) (3) (1) (2) (3) (2) (2) Amount of solderpowder 90   90   90   90   90   90   90   90   90   (parts by weight)Result of Evaluation Wettability 1   1   2   4   2   3   4   4   4  Solder ball test 2   2   4   5   3   4   5   5   5   Void formationpassed passed failed failed failed failed failed failed failedInsulation Initial (b) (b) (b) (b) (b) (b) (b) (a) (a) Performance After100 hrs (b) (b) (b) (b) (b) (b) (b) (a) (a) Storage Initial 400   400    450    500    420    470    530    390    420    stability After100 hrs 490    490    610    — 490    670    — 420    450    (Pa · s)Viscosity  1.02  1.02  1.04 —  1.17  1.43 —  1.08  1.07 Increase RatioResidue after reflow — — — — — — — (a) (a) Residue cleanability (1) (b)(a) (a) — — — — — — Residue cleanability (3) — — — — (b) (b) — — —

Example 3-1

[0166] As shown in FIG. 2, each flux 21 prepared in Examples 1-1 to 1-17was applied thinly to a wiring pattern formed on ceramic substrate 20with Cu conductor 21 at 250 μm pitch. Flip chip IC 23 provided withsolder bumps 22 at 250 μm pitch (provided with 224 bumps) was mounted onthe wiring using a high precision mounter. Electrodes of the flip chipIC 23 were formed by soldering Sn/Ag3.0/Cu0.5 (weight ratio) on Cubumps. After the mounting, the assembly was subjected to reflow in theair at the peak temperature of about 245° C. As a result, all of thefluxes provided good soldering even at such a fine pitch as 250 μm.

Example 3-2

[0167] An Example of a soldering method by means of flow soldering in aflow process is shown in FIG. 3. Shrink-type IC 31 having terminal 1 a,chip component 32 such as a ceramic capacitor having electrodes 2 a, andcircuit component 33 having component terminals 33 a were temporarilybonded to substrate 30 as shown in FIG. 3(a), and each flux prepared inExamples 1-1 to 1-17 was applied over the entire rear surface of thesubstrate 30. Then the substrate 30 was subjected to pre-heating step atabout 150° C., passed through a flow soldering chamber to be broughtinto contact with a molten solder at about 240° C., and dried with afan. As a result, each connecting terminal of the components of thecircuit was excellently soldered with solder 34 by flow soldering asshown in FIG. 3(b).

Example 3-3

[0168] The flux prepared in Example 1-17 was applied to wiring of a Ag-or Cu-based thick film provided on a ceramic substrate. As illustratedin FIG. 4, substrate 40 was vertically immersed into vessel 41containing molten solder 41 a of a composition Sn/Ag2.0/Pb36.0 (weightratio) maintained at about 235° C. After about two-second immersion, thesubstrate 40 was drawn out of the molten solder at an angle of about 45degrees with respect to the liquid level, with a little material left onits surface. Subsequently, the substrate 40 was again verticallyimmersed in the vessel 41 for about three seconds, and slowly drawn outat an angle of about 45 degrees with respect to the liquid level. Withsome materials, little flux remained on the substrate surface, and thesolder was excellently applied to the substrate 40 thus dipped,irrespective of the shape and size of the lands thereon. Even ifremained, the material was in a trace amount, and removable with ethanolor the like, or decomposed and evaporated in the subsequent mounting ofthe components and reflow, leaving no residue in the end. Thus no-cleansoldering was realized.

[0169] The results of thermogravimetric analysis of (S-4) and (A-1) usedin the flux prepared in Example 1-17 are shown in FIG. 5. From thisfigure, it is understood that (S-4) and (A-1) reached 100% weight lossnear 250° C., and thus the flux with these materials leavessubstantially no residue after reflow.

Example 3-4

[0170] Each solder paste prepared in Examples 2-1 to 2-23 was printed ondesired positions on wiring provided on a substrate, and an LSI, a chipresistor, and a chip capacitor were placed on the solder paste. Theassembly was heated with a reflow heat source for soldering. A hot blaststove was used as the reflow heat source. With the Sn63/Pb37 (weightratio) solder paste, the reflow conditions included the pre-heattemperature of 130° C., the pre-heating duration of 65 seconds, the toptemperature of 220° C., and the holding time at 200° C. or higher of 30seconds. With the Sn/Ag2.9/Cu0.5 (weight ratio) solder paste, the reflowconditions included the pre-heat temperature of 150 to 170° C., thepre-heating duration of 110 seconds, the top temperature of 245° C., andthe holding time at 200° C. or higher of 50 seconds. With theSn/Zn8.0/Bi3.0 (weight ratio) solder paste, the reflow conditionsincluded the pre-heat temperature of 140 to 160° C., the pre-heatingduration of 65 seconds, the top temperature of 230° C., and the holdingtime at 200° C. or higher of 30 seconds. After the reflow, the substratewas cooled. It was observed that the reflow soldering was in success.

What is claimed is:
 1. A soldering flux composition comprising at leastone compound having at least one blocked carboxyl group selected fromthe group consisting of: compound (X) obtained by reaction of acarboxylic acid compound and a vinyl ether compound; compound (Y)obtained by reaction of a carboxylic acid anhydride compound and ahydroxy vinyl ether compound; and compound (Z) obtained by reaction ofan acid anhydride and a polyhydric alcohol, followed by additionpolymerization with a divinyl ether compound; wherein said solderingflux composition is non-curing.
 2. The composition of claim 1, whereinsaid compound (X) has an acid number of not larger than 5 mgKOH/g, saidcompound (Y) has an acid number of not larger than 20 mgKOH/g and aweight average molecular weight of 300 to 100000, and said compound (Z)has an acid number of not larger than 10 mgKOH/g and a weight averagemolecular weight of 500 to
 500000. 3. The composition of claim 2,wherein said compound (X) is at least one compound selected from thegroup consisting of compounds represented by the formulae (1) and (2),said compound (Y) is a compound represented by the formula (3), and saidcompound (Z) is a compound represented by the formula (4):

wherein in the formula (1), x is an integer of 1 to 6, A¹ stands for acarboxyl acid residue without —(COO—)_(x), and Z¹ stands for the formula(1-1) or (1-2):

wherein R¹, R², R³, R⁵, and R⁶ each independently stands for a hydrogenatom or an organic group having 1 to 50 carbon atoms, R⁴, R⁷, and R⁸each independently stands for an organic group having 1 to 50 carbonatoms, and Y¹ and Y² each independently stands for an oxygen or sulfuratom; in the formula (2), A²stands for a carboxylic acid residue without—(COO—)_(m), Y³ and Y⁴ each independently stands for an oxygen or sulfuratom, R⁹ stands for an organic group having 1 to 50 carbon atoms, m isan integer of 1 to 6, and n is an integer of 0 to 5;

wherein R¹⁰ stands for a substituted or unsubstituted divalent aliphaticor aromatic group having 1 to 50 carbon atoms, R¹¹ stands for a divalenthydrocarbon group or glycol residue having 1 to 50 carbon atoms, Y⁵stands for an oxygen or sulfur atom, and s is an integer of 1 to 500;

wherein R¹², R¹³, and R¹⁴ each independently stands for a divalentorganic residue, Y⁶ stands for an oxygen or sulfur atom, and t is aninteger of 1 to
 500. 4. The composition of claim 1 further comprising atleast one member selected from the group consisting of a latent heatcatalyst, a photocatalyst, an activator, a thixotropic agent, anantioxidant, a rust preventive agent, and a solvent.
 5. The compositionof claim 1 further comprising a compound having one reactive functionalgroup in a molecule capable of forming a chemical bond with a carboxylgroup upon heating.
 6. A solder paste comprising a flux composition ofclaim 1 and solder powder.
 7. A method of soldering comprising the stepsof: (A) providing a flux composition of claim 1 on an electrode portionof a substrate; (B) providing a solder bumped electronic component; (C)placing said electronic component provided in step (B) on said substrateobtained in step (A); and (D1) subjecting the substrate with theelectronic component obtained in step (C) to reflow for mounting.
 8. Amethod of soldering comprising the steps of: (A) providing a fluxcomposition of claim 1 on an electrode portion of a substrate; and (D2)supplying solder onto the substrate with the flux composition obtainedin step (A), by flowing or dipping.
 9. A method of soldering comprisingthe steps of: (X) printing a solder paste of claim 3 on an electrodeportion of a substrate; (Y) placing an electronic component on saidsubstrate obtained in step (X); and (Z) subjecting said substrate withthe electronic component obtained in step (Y) to reflow for mounting.